GeoGraph - photograph every grid square

This pattern of raised ridges occurs on one face of a large detached block of sandstone beneath the crags of Cwar y Gigfran. It was probably the underside of the block when it was still in position. The largest ridges are up to 3cm across, 1.5cm high and over 2m long. I interpret them as casts of cracks which appeared under a hot tropical sun as a layer of mud dried after a flood. A subsequent flood washed sand over and into the cracks, turned to stone over succeeding millennia and left us with this fabulous pattern. Britain lay in the southern tropics when the Old Red Sandstone of the Brecon Beacons was being deposited. Though this spot is just outside Fforest Fawr Geopark, there's more at Link